1. Field of the Invention
The present invention relates to a double-seat valve with an upper valve stem and a lower valve stem in a valve housing. The double seat valve also has pipeline connections located one above the other and a valve sealing or mating seat located between the upper pipeline connections and the lower pipeline connections for the valve stems. The valve stems can be actuated independently of one another and can be moved onto a balance diameter in the valve housing. The valve stems, which are equipped on the ends with valve sealing or mating bodies corresponding to one another, form a leakage space which is open on the bottom, and the valve sealing bodies are each surrounded by at least one seal. Each at least one seal is in contact on the balance diameter against the valve sealing seat, and one of the valve sealing bodies has a center seal against which the other valve sealing body is in contact when the valve stems are moved toward one another in the open position. In the context of this invention, the term "balance diameters" means that the valve stems and the valve sealing bodies are each guided on identical diameters or almost identical diameters, maintaining a fitting gap in the valve housing.
2. Background Information
A known double-seat valve is described in European Patent No. 0 140 432, for example, in which the center seal is located on the plate-like valve sealing body of the lower valve stem. This device describes a significantly smaller diameter than the balance diameter, on which the seals which surround the upper valve sealing body and the lower valve sealing body are located. Such an arrangement of the center seal is problematic, in particular if the two valve stems or their valve sealing bodies are in the open position, and thus the upper pipeline connections are in communication with the lower pipeline connections via the open valve sealing seat. When the valve stems are in the open position and the valve sealing bodies are moved toward one another, the leakage space must be closed with respect to the communicating pipeline connections and the medium being transported in them. If, however, a pressure fluctuation or pressure hammer which is propagated via the medium occurs when the valve components are in this position, there is a danger that the upper valve stem and the lower valve stem and/or their valve sealing bodies will be pushed together as a result of the incorrectly balanced center seal, and medium will flow downward via the leakage space.
A further problem can be seen in the fact that the known double seat valve must be completely disassembled when it becomes necessary to replace the seal. That is because, despite the fact that the valve stems with the valve sealing bodies can be removed from the valve housing, the center seal, because its diameter is very much smaller than the balance diameter, cannot be extracted over the lower or upper valve stems or their valve sealing bodies, and a new center seal pulled on, because the seals used do not have the required elasticity. In addition, the center seal is not accessible without disassembling the valve sealing bodies in question.
The present invention proposes to solve these problems.